71 lines
2.0 KiB
Plaintext
71 lines
2.0 KiB
Plaintext
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Lock file support
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=================
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The ZODB lock_file module provides support for creating file system
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locks. These are locks that are implemented with lock files and
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OS-provided locking facilities. To create a lock, instantiate a
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LockFile object with a file name:
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>>> import zc.lockfile
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>>> lock = zc.lockfile.LockFile('lock')
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If we try to lock the same name, we'll get a lock error:
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>>> import zope.testing.loggingsupport
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>>> handler = zope.testing.loggingsupport.InstalledHandler('zc.lockfile')
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>>> try:
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... zc.lockfile.LockFile('lock')
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... except zc.lockfile.LockError:
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... print("Can't lock file")
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Can't lock file
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.. We don't log failure to acquire.
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>>> for record in handler.records: # doctest: +ELLIPSIS
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... print(record.levelname+' '+record.getMessage())
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To release the lock, use it's close method:
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>>> lock.close()
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The lock file is not removed. It is left behind:
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>>> import os
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>>> os.path.exists('lock')
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True
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Of course, now that we've released the lock, we can create it again:
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>>> lock = zc.lockfile.LockFile('lock')
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>>> lock.close()
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.. Cleanup
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>>> import os
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>>> os.remove('lock')
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Hostname in lock file
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=====================
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In a container environment (e.g. Docker), the PID is typically always
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identical even if multiple containers are running under the same operating
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system instance.
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Clearly, inspecting lock files doesn't then help much in debugging. To identify
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the container which created the lock file, we need information about the
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container in the lock file. Since Docker uses the container identifier or name
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as the hostname, this information can be stored in the lock file in addition to
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or instead of the PID.
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Use the ``content_template`` keyword argument to ``LockFile`` to specify a
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custom lock file content format:
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>>> lock = zc.lockfile.LockFile('lock', content_template='{pid};{hostname}')
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>>> lock.close()
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If you now inspected the lock file, you would see e.g.:
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$ cat lock
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123;myhostname
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